Among the nuclear reactors of the future, the Fast Neutron Reactor (FNR), which uses helium as the coolant gas (the so-called “He-GFR” reactor), may be mentioned. This reactor is a so-called “high-temperature” reactor because during operation the temperature of its core generally lies in the range between 800° C. and 1200° C.
As described in patent application EP 1 913 600, a nuclear fuel cladding employed in such a reactor may be provided as a plate, a cylinder, a sphere or a network of cavities.
When subjected to the above-mentioned temperature conditions, this cladding requires the use of high-melting point refractory materials (in order to ensure sufficient thermomechanical stability to maintain the fuel within the cladding) and should have a high thermal conductivity under irradiation (in order to optimally transfer the generated thermal energy towards the coolant gas during operation of the nuclear reactor).
Ceramics, although they meet these criteria, are generally too brittle to withstand the operating conditions of a nuclear fuel cladding.
Indeed, fission reactions within the nuclear fuel generate solid and gaseous fission products which cause cladding swelling. When subjected to such loads, the ceramics that form the cladding may break-up and cause a loss of fuel confinement.
In order to avoid such a loss, it would therefore be beneficial to use a ceramic matrix composite (CMC) material of the SiCf/SiC type, in order to achieve improved mechanical properties. Such a material is generally made of a two-dimensional or three-dimensional arrangement of silicon carbide fibers (referred to as SiCf), which contributes to the reinforcement of the SiC ceramic matrix in which it is incorporated.
However, for a given temperature, the thermal conductivity of CMCs of the SiCf/SiC type may strongly decrease after it has been subjected to irradiation.
During the operation of a “He-GFR” nuclear reactor subjected to high temperatures, such CMCs therefore prove to be inappropriate for the removal of thermal energy from the nuclear fuel cladding towards the coolant gas.